The nature of video and audio teleconferencing creates a well known problem with the audio: acoustic echo return from the remote site, as shown in FIG. 1. Without an active cancellation system, the conferencing room becomes unusable due to distracting audio feedback from the remote site. In FIG. 1, at the remote conferencing room (site) 10, the loudspeaker 12 audio output inevitably is picked up by the room microphone 14 and returns via conferencing link 22 to the local room (site) 16 via its loudspeaker 18 as an undesirable “echo” picked up by its microphone 20, for repeating via return link 26.
Most present audio or video conferencing systems that attempt to deal with this problem employ an active filtering device known as an AEC or “Acoustic Echo Canceller” to handle unwanted echo. This uses a digital signal processing (DSP) electronic cancellation of unwanted echo (or an analog signal processing version), performed at the remote site for the local room.
In other words, the local listener ideally hears no echo because the remote room's AEC unit cancels the echo for the local listener. This cancellation is mirrored by the local room's AEC unit for the remote listener.
Current AEC devices have several significant limitations: They do not take network and compression latency (delay) into account, and therefore a “lag” in the echo cancellation sometimes causes echoes. They rely on actual microphone input (the user's voices) to model and create a “simulated echo” which is then used to cancel the actual echo. This approach fails when a “double-talk”situation happens (when users in both rooms talk at the same time). They are not optimized for a multi-point connection (one to many rooms) where different delays and different room acoustic characteristics are present.